You need to investigate, and measure Allen Variance, a better
indication of the quality of an oscillator. What you will most
likely find is the GPS disciplined oscillator, though very good
in terms of "accuracy", is poor for short term Allen Variance,
and that the HP 107 is very good for short term Allen Variance,
and poor for long term Allen Variance.
This path is well trodden for a group of people that are known
as timenuts, and they have a group of their own where they
discuss such things.
-Chuck Harris
jtml@... [hp_agilent_equipment] wrote:
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We need extreme freq stability for our master freq reference for a particle accelerator that is 770 meters long. The original 46 year old oscillator was first a HP107BR special that was at 6.289xxxx MHz, then multiplied up with a TCI multiplier assembly. Later it was HP105B, again special crystal in double oven setup. Backup was a Vectron oscillator. Four years ago, a digital engineer replaced the crystal sources with a Meridian End Run GPS-disciplined oscillator and a TCI phase locked assembly with multipliers. This is used to generate a 100.625 Mhz, 201.25 Mhz and 805 MHz reference. With phase stability giving trouble, I took to comparing the GPS ultra-stable reference to the HP105B, 10 MHz vs 6.289xxxx. I used a HP 5372A dual channel frequency analyzer, and recorded histograms and stats of each oscillator. The GPS-disciplined oscillators are clearly inferior by a factor of 10 for medium term stability over a few hours. Two of them were tested. Then I found an old Racal Rubidium oscillator in VXI format. It works great. The moral of this story is, specs on paper aren't always enough. The GPS oscillators claimed 10^-11 and such, over 24 hours. But over shorter term even, they jumped around and covered a few millihertz spread. Stanford Research has a nice crystal oscillator that is also available as a Rubidium oscillator option. These are not very expensive.
